Final answer:
Option c)Nasir Khusraw was the major Muslim intellectual, philosopher and Shia Ismaili Da'i of the 11th century.
Step-by-step explanation:
The major Muslim intellectual, philosopher, and traveller of the 11th century who was a prominent Shia Ismaili Da'i is c)Nasir Khusraw.
He was a Persian polymath whose comprehensive scholarship spanned numerous subjects, including philosophy, medicine, astronomy, and poetry. His influential teachings and writings, especially in philosophy, were vital in bridging the formative and creative phases of Islamic thought during the Islamic Golden Age. However, his specific role as an Ismaili Da'i sets him apart from others like Ibn Sina (Avicenna) and Al-Ghazali, who were also significant scholars of the time but not Ismaili Da'is.